The invention relates to photoflash lamps and particularly to photoflash lamps which are electrically activated. Even more particularly, the invention relates to flash lamps of the above variety wherein a single lead is utilized.
Most prior art flash lamps which are electrically-activated require at least two conductive leads which extend within the lamp's glass envelope. Examples are illustrated in U.S. Pat. Nos. 3,959,860 (Schindler), 3,941,555 (Anderson et al) and 3,897,196 (Sanders et al). These leads provide the needed current path to the lamp's primer material which, when activated, ignites a quantity of combustible material (e.g. shredded zirconium) to produce the desired highly intense flash of light.
Understandably, the requirement for using two leads substantially limits attempts to minimize the spacing requirements in designing the above lamps. The requirement for a second lead member also increases the opportunity for an improper seal between this member, which is normally metallic, and the envelope, which is typically of glass material.
At least one early attempt was made to produce a single lead, electrically fired flash lamp. As shown in U.S. Pat. No. 2,768,517 (R. H. Atkinson et al), a single aluminum lead was located within a plastic base and projected within a glass envelope. Successful activation was only possible when an extremely high potential (e.g. 10,000 to 20,000 volts) was applied across the lead and a spaced reflector was capacitively joined to the lamp's internal combustible material (e.g. aluminum foil). It was further necessary in U.S. Pat. No. 2,768,517 to provide a dielectric layer on the external surface of the portion of the lead which extended within the envelope. Crevices were required in this layer to provide a path for the spark discharge which then passes through spaced apertures in a porous primer. As a result of the above requirements, particularly the need for an activating potential in excess of 10,000 volts, most modern day engineering efforts have been directed toward the aforementioned dual lead embodiments. The disadvantages associated therewith are apparently more tolerable by engineering standards in comparison to the problems inherent in supplying excessively high quantities of electrical energy.
It is believed, therefore, that a single lead, electrically-activated flash lamp which can be successfully fired at potentials substantially less than those required in the aforedescribed prior art would constitute a significant advancement in the art.